The present invention relates to a thermal ink jet print head.
A print head for a thermal ink jet printer is known in which a multi-layer print plate carrying the nozzles and electrical terminals for pilot control thereof is fixed to an end wall of a reservoir containing a spongy body impregnated with ink.
The nozzles are hydraulically connected to the interior of the reservoir by way of a supply conduit passing through the plate and disposed at a position corresponding to an opening in the end wall of the reservoir. The electrical terminals of the print plate are soldered or welded to corresponding conductors of a flat cable fixed to the end wall on the outside of the reservoir. The flat cable carries conductive areas or pads which can be connected under the effect of pressure to corresponding fixed terminals of the printer.
The reservoir with the plate which is fixed with respect thereto form an integrated printing and supply unit which is mounted removably on the carriage of the printer. When the ink is exhausted the integrated unit is replaced by another unit loaded with ink.
As will be apparent, the ink always fills the nozzles and always remains in contact with the internal metal layers of the plate. During long periods of storage or inactivity of the integrated head, it may be found that the arrangement suffers from blockages of nozzles by virtue of drying of the ink or corrosion phenomena in respect of internal layers of the plate, with a consequential deterioration in the quality of printing and a reduction in the level of efficiency of the head itself. In addition since the life of a print head is much longer than the period for which the ink contained in the reservoir lasts, each time that the integrated unit is replaced, it is necessary to throw away a print plate which is still effective.
An object of the present invention is that of providing a thermal ink jet print head which is free from the above-discussed disadvantages.
More particularly another object of the present invention is to make complete use of the printing plate for the whole of its period of effectiveness.
A further object of the present invention is to increase the period of effectiveness of the printing plate, keeping it free from ink during the periods of printing inactivity in order to minimise the risk of corrosion by the ink.